Copper, copper alloy, and manufacturing method therefor

ABSTRACT

Copper and copper alloy comprises: a structure having fine crystal grains with grain size of 1 μm or less after a final cold rolling with a reduction η, wherein η is expressed in the following formula and satisfying η≧3; and an elongation of 2% or more in a tensile test. 
     η=ln( T   0   /T   1 ) 
     T 0 : plate thickness before rolling, T 1 : plate thickness after rolling.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to copper and to copper alloyshaving fine crystal grains, and relates to a manufacturing methodtherefor, and more particularly, the resent invention relates to atechnology for enhancing the characteristics in bending or other workingwhen used for electronic devices such as terminals, connectors, and leadframes for semiconductor integrated circuits.

[0003] 2. Description of the Related Art

[0004] Recently, electronic devices such as terminals and connectors andtheir parts are reduced in size and thickness, and copper and copperalloy used as materials thereof are demanded to have high strength. Interminal and connector material, the contact pressure must be increasedin order to maintain electrical connections, and a high strengthmaterial is essential for this purpose. In a lead frame, because thesemiconductor circuit is highly integrated, there is an increasingdemand for multi-pin structures and thin wall thicknesses. Accordingly,to prevent deformation while conveying or handling the lead frame, therequired strength level is progressively increasing.

[0005] Moreover, along with the trend in size-reduction of electronicdevices and components, a higher degree of freedom of formingperformance is demanded, and workability of connector materials isbecoming important, and in particular, an excellent bending propertiesare required. In the outer lead of the semiconductor lead frame, anexcellent bending properties are also needed in the case of gull-wingform bending processes.

[0006] In order to obtain an excellent bending properties not causingcracks in the bent part when a material is bent and deformed, it isnecessary to enhance material ductility or to decrease grain size.Furthermore, for the copper alloy used for electronic device, a functionfor allowing the heat generated during power feed to escape to theoutside is needed, aside from a function of transmitting an electricsignal, and a high heat conductivity is required in addition toelectrical conductivity. In particular, to cope with the recent trend ofhigher frequency electrical signals, the demand for higher electricalconductivity is mounting.

[0007] Electrical conductivity of copper alloy is inversely related tostrength, and when an alloying element is added to enhance the strength,the electrical conductivity is lowered, and therefore alloys whichcompromise strength and electrical conductivity or price have been used,depending on the application. So far, alloys for enhancing the strengthand electrical conductivity have been intensively developed, andgenerally, copper alloys of precipitation reinforced type containingsecond phase particles such as Cu—Ni—Si alloy or Cu—Cr—Zr alloy havecome to be used as high functional materials which is superior inbalance between both.

[0008] Thus, for mechanical characteristics of copper or copper alloysfor electronic devices, high strength and excellent workability aredesired. However, first of all, strength and ductility are inverselyrelated to each other, and in each alloy system, when rolling isprocessed in order to increase the strength by work hardening, theductility declines, and preferable workability is not obtained byrolling alone. On the other hand, by reducing the grain size, increasein strength as indicated by the Hall-Petch relation is expected, and italso leads to improvement of bending properties, and hence it wasgenerally controlled to reduce the grain size during annealing andrecrystallization.

[0009] In this method, however, when the annealing temperature islowered in order to reduce the grain size, non-crystallized grainsremain in part, and there is substantially a limit to obtainingrecrystallized grains of about 2 to 3 μm, and a technique for furtherreducing the grain sizes has been demanded. Furthermore, byrecrystallization alone, the strength level is usually low, and it isnot practical, and therefore a certain rolling process is needed in alater step, which has led to reduction of ductility. Accordingly,generally after rolling process, a process of stress relief annealingwas needed to recover the ductility. This process, however, causeslowered strength once obtained in the rolling process, and sufficientductility is not obtained after stress relief annealing, and it wasdifficult to satisfy the recent extremely severe demand for bendingdeformation performance.

[0010] More recently, instead of an annealing process, methods ofobtaining fine crystal grains and high ductility by working materials bystrong shearing have been studied and reported, for example, by Ito etal. (ARB (Accumulative Roll-Bonding, J. of Japan Society of Metallurgy,54 (2000), 429), and Hotta et al. (ECAP (Equal-Channel Angular Press),Metallurgy seminar text: Approach to fine crystal grains (2000), JapanSociety of Metallurgy, 39). In these processing methods, however, a massquantity sufficient to be used as materials for electronic devicescannot be manufactured, and there are not suited to industrialproduction.

SUMMARY OF THE INVENTION

[0011] The inventors have accumulated extensive research to solve theseproblems, and they have discovered that fine crystal grains at a levelnot known thus far can be obtained by controlling the conditions of therolling process instead of the conditions of the annealing. That is, inthe structure of a material cold rolled with an ordinary cold rollingreduction, when recrystallized by subsequent annealing, the decrease indislocation density occurs discontinuously when the recrystallized grainboundaries pass a cell, and large crystal grains of uneven size areproduced intermittently. This is called static recrystallization.According to the research by the inventors, by extremely increasing thereduction of cold rolling, dynamic recrystallization, usually exhibitedin high temperature regions, was also found to occur in cold rolling,and dynamic continuous recrystallization is exhibited as the subgrainsformed during processing are transformed into high angle grainboundaries. By making use of this mechanism, round and uniform crystalgrains of grain size of 1 μm or less are obtained. According to thismethod, fine crystal grains can be obtained without sacrificing thestrength in order to prevent reduction of ductility, and it is alsofound that an elongation of 2% or more is obtained even immediatelyafter final cold rolling, and an allowable bending properties areobtained by cold rolling alone. Furthermore, by adding stress reliefannealing processing after final cold rolling, the elongation is furtherenhanced, and thus is applicable also in the case exposed to extremelysevere bending. According to such a manufacturing method, moreover,materials for electronic devices can be mass produced industrially.Continuous recrystallization is explained in detail below.

[0012] The present invention is made on the basis of these findings, andprovides copper and copper alloy comprising: a structure having finecrystal grains with grain size of 1 μm or less composed of crystal grainboundaries mainly formed of curved portions after a final cold rolling,the structure obtained by dynamic continuous recrystallization caused bythe final cold rolling, and an elongation of 2% or more in a tensiletest.

[0013] The present invention also provides a manufacturing method forcopper and copper alloy, the method comprising: a final cold rollingwith a reduction (true stress) η, wherein η is expressed in thefollowing formula and satisfying η≧3, thereby obtaining a structurehaving fine crystal grains with grain size of 1 μm or less after thefinal cold rolling, and

[0014] an elongation of 2% or more in a tensile test.

η=ln(T ₀ /T ₁)

[0015] T₀: plate thickness before rolling, T₁: plate thickness afterrolling.

[0016] The reasons for setting these numerical values are explainedbelow together with the functions of the invention.

[0017] A. Reduction of Final Cold Rolling, Elongation, and Grain Size

[0018] In order to obtain a favorable bending properties in a materialsubjected to final cold rolling alone, a high ductility is essential. Inorder to obtain the favorable bending properties not causing cracking inthe bent portion, a fracture elongation in a tensile test is required tobe 2% or more at a gauge length of 50 mm. In order to obtain a ruptureelongation of 2% or more in the state of final cold rolling, the grainsize after final cold rolling must be 1 μm or less. Thus, sufficientelongation is obtained in the cold rolled state by decreasing the grainsize, which is because dislocations are piled-up in the grain boundarywhen continuous recrystallized grains are formed, and a grain boundarystructure of a non-equilibrium state is formed and a grain boundarysliding is expressed, thereby enhancing the ductility.

[0019] The grain size and elongation after final cold rolling varydepending on the cold rolling reduction. The cold rolling reduction(true stress) η by final cold rolling process until reaching the productplate thickness is expressed in the formula below.

η=ln(T ₀ /T ₁₎

[0020] T₀: plate thickness before rolling, T₁: plate thickness afterrolling.

[0021] In this case, when the value of η is small, a rolled structureremains, and clear fine crystal grains are not obtained, or if they areobtained, the grain size is large, and the grain boundary sliding doesnot take place, and favorable ductility is not obtained. According tothe research by the inventors, it is known that the value of η should be3 or more in order to obtain a fine grain size of 1 μm or less.

[0022] The structure of a material cold rolled by a conventionalordinary cold rolling reduction sometimes had a cell structure due tomutual entangling of dislocations introduced in the crystal grains. Inthis case, however, since the misorientation among neighboring cells issmall, that is, 15° or less, properties as crystal grain boundary arenot realized. Accordingly, as shown in FIG. 1, when recrystallized byannealing after cold rolling, as mentioned above, static crystallizationtakes place, that is, large crystal grains of uneven size are formedintermittently.

[0023] In contrast, by setting the extremely high cold rollingreduction, fine crystal grains are obtained. That is, at a very highcold rolling reduction, numerous regions locally shearing deformed occurin the matrix in the entire material and thus subgrain structuresgreatly grow. As a result, as shown in FIG. 1, dislocations areintroduced in order to compensate the large misorientation between thematrix and the subgrain, and they are piled-up in the grain boundary. Inthis case, crystal grain boundaries having a large misprientation of 15°or more (high angle grain boundary) are generated. That is, the subgrainstructure which has been initially a substructure of crystal grains isdirectly formed as crystal grains. In this case, the crystal grainboundary is largely different from the case of the staticrecrystallization, and there is no linearity in the grain boundary, andit is a feature that a crystal grain boundary mainly composed of curvedportions is formed. This dynamic continuous recrystallization is mostlyformed in cold rolling. It is also known that a clearer high angle grainboundary is grown by annealing at intentional low temperatures andbringing it into an ordinary recovery regime. In this case, it is foundthat the ductility is further enhanced as described below.

[0024] In this mechanism, if second phase particles such as precipitatesand dispersoids are present in the Cu matrix, dislocations introduced byplastic stress due to rolling are accumurated around the second phaseparticles by forming dislocation loops or the like, and the dislocationdensity is substantially increased. In this condition, the particle sizeof the subgrains becomes much finer, and the strength becomes higher. Inthe final cold rolling, unless recovered or recrystallized by annealingin an intermediate processing, cold rolling may be performed by pluralrolling machines by exchanging rolling machines depending on the rangeof plate thickness, or pickling or polishing may be performed in orderto control the surface properties.

[0025] B. Stress Relief Annealing

[0026] When the material after final cold rolling is further annealedfor stress relief, the ductility is enhanced, and a further preferablebending properties are obtained. As annealing conditions, it isnecessary to set adequate annealing conditions to such an extent thatthe product value will not be lost due to extreme decline of strength.The annealing condition differs with the alloy system, but by selectingan appropriate annealing condition in a temperature range of 80 to 500°C. and in a range of 5 to 60 minutes, an elongation of 6% or more may beeasily obtained, and it is applicable to a severe bend forming.

[0027] Preferred examples of copper alloy of the invention includeCu—Ni—Si alloys having precipitates of intermetallic compounds of Ni andSi such as Ni₂Si, and the copper alloys comprise Ni: 1.0 to 4.8 mass %,Si: 0.2 to 1.4 mass %, and the balance of Cu. The invention alsoincludes Cu—Cr—Zr alloys having precipitates of pure Cr grains andintermetallic compounds of Cu and Zr, and the copper alloys comprise Cr:0.02 to 0.4 mass %, Zr: 0.1 to 0.25 mass %, and balance of Cu. Thesecopper alloy may be added with subsidiary components such as one or moreof Sn, Fe, Ti, P, Mn, Zn, In, Mg and Ag in a total amount of 0.005 to 2mass %. Moreover, copper alloys having second phase particles such asother kinds of precipitates and dispersed particles may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

[0028]FIG. 1 is a schematic diagram for explaining the recrystallizationprocess.

[0029]FIG. 2 is a transmission electron microscope photograph showing astructure of an alloy in an example of the invention.

[0030]FIG. 3 is a transmission electron microscope photograph showing astructure of an alloy in a comparative example of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] (Embodiments)

[0032] Effects of the invention are more specifically described below byreferring to preferred embodiments. First, using electric copper oroxygen-free copper as material, a specified amount of the material wasput in a vacuum melting furnace, together with other additive elements,if necessary, and ingots of the chemical composition shown in Tables 1to 3 were obtained by casting at the molten metal temperature of 1250°C. Table 1 shows the compositions of Cu—Ni—Si alloys, Table 2 shows theCu—Cr—Zr alloys, and Table 3 shows other copper alloys. TABLE 1 Cu—Ni—Sialloy Final Rolling Condition Product Properties Chemical compositionOriginal Plate Final Plate Tensile Rupture Cu and Thickness ThicknessCold Rolling Grain Size Strength Elongation Bending Conductivity Ni SiImpurities (mm) (mm) Reduction (μm) (MPa) (%) Properties (% IACS)Example of Invention 1 3.02 0.67 Balance 3.30 0.15 3.1 0.20 820 3.7 ◯ 482 2.75 0.59 Balance 3.80 0.15 3.2 0.15 810 3.8 ◯ 50 3 3.18 0.62 Balance3.65 0.15 3.2 0.15 830 4.5 ◯ 49 4 3.30 0.70 Balance 3.40 0.15 3.1 0.20820 3.8 ◯ 48 5 2.60 0.55 Balance 3.00 0.15 3.0 0.40 800 2.3 ◯ 51Comparative Example 6 3.21 0.59 Balance 1.85 0.15 2.5 2.00 800 1.2 X 487 2.80 0.58 Balance 1.10 0.15 2.0 Rolled Structure 790 0.8 X 50 8 3.150.64 Balance 2.50 0.15 2.8 1.35 800 1.8 X 47

[0033] TABLE 2 Cu—Cr—Zr alloy Final Rolling Condition Product PropertiesChemical Composition Original Plate Final Plate Cold Tensile Rupture Cuand Thickness Thickness Rolling Grain Size Strength Elongation BendingConductivity Cr Zr Zn Impurities (mm) (mm) Reduction (μm) (MPa) (%)Properties (% IACS) Example of Invention  9 0.21 0.08 — Balance 3.250.15 3.1 0.30 610 3.5 ◯ 80 10 0.18 0.10 — Balance 3.50 0.15 3.1 0.30 6003.9 ◯ 82 11 0.23 0.14 — Balance 3.80 0.15 3.2 0.25 620 4.8 ◯ 79 12 0.180.07 0.22 Balance 3.75 0.15 3.2 0.25 610 5.0 ◯ 78 13 0.24 0.11 0.18Balance 3.10 0.15 3.0 0.35 620 2.8 ◯ 77 Comparative Example 14 0.20 0.11— Balance 1.15 0.15 2.0 Rolled 590 0.8 X 80 Structure 15 0.18 0.08 —Balance 2.60 0.15 2.9 1.20 600 1.7 X 81 16 0.23 0.09 0.19 Balance 1.500.15 2.3 1.40 590 1.3 X 78

[0034] TABLE 3 Manufacturing conditions of other alloys of the inventionand comparative examples Final Rolling Condition Original Cold ChemicalComposition (w %) Plate Final Plate Rolling Cu and Thickness ThicknessReduc- Sn Cr Zr Ni Si Fe Ti P Mn Zn In Mg Ag Impurities (mm) (mm) tionExample of Invention 17 — — — — — — — — — — — — — Tough 3.80 0.15 3.2Pitch Copper 18 — — — — — — — — — — — — — Oxygen- 3.40 0.15 3.1 freeCopper 19 — — — — — — — — — — — — 0.03 Balance 3.50 0.15 3.1 20 5.12 — —— — — — 0.02 — — — — — Balance 3.10 0.15 3.0 21 — 0.18 — — — — — — — — —— — Balance 3.25 0.15 3.1 22 0.22 0.28 — — — — — — — 0.19 — — — Balance3.75 0.15 3.2 23 — — 0.08 — — — — — — — — — — Balance 3.65 0.15 3.2 24 —0.18 0.11 — — 0.61 0.37 — — — — — — Balance 3.00 0.15 3.0 25 — 0.22 0.13— — — — — — — 0.04 — — Balance 3.10 0.15 3.0 26 — 0.26 0.11 — 0.02 — — —— — — 0.04 — Balance 3.75 0.15 3.2 27 — — — 2.61 0.51 — — — — 0.29 — — —Balance 3.70 0.15 3.2 28 0.51 — — 2.11 0.48 — — — — 0.48 — — — Balance3.65 0.15 3.2 29 — — — — — 1.81 — 0.15 — — — 0.02 — Balance 3.30 0.153.1 30 — — — — — 2.43 — 0.03 — 0.12 — — — Balance 3.75 0.15 3.2 31 — — —— 0.04 3.01 — 0.26 0.03 — — — — Balance 3.80 0.15 3.2 32 — — — — — —2.95 — — — — — — Balance 3.50 0.15 3.1 Com- parative Example 33 — 0.180.09 — — — — — — 0.12 — — — Balance 1.10 0.15 2.0 34 — — — 3.12 0.67 — —— — 0.14 — — — Balance 2.50 0.15 2.8

[0035] These ingots were hot rolled at a temperature of 950° C. intoplates of 10 mm in thickness. The oxide layer of the surface layer wasremoved by mechanical scalping, and the plates were cold rolled to athickness of 5 mm, and a solid solution treatment was applied in thecase of age precipitation type copper alloy, and recrystallizationannealing was applied once in the others. By further cold rolling,plates of an intermediate thickness of 1.1 to 3.8 mm were obtained, andat this plate thickness, further, aging treatment or secondrecrystallization annealing was performed. In the case of agingtreatment, the aging temperature was adjusted so that the productstrength would be highest in each alloy composition, or in the case ofrecrystallization, the temperature condition was adjusted so that thegrain size would be 5 to 15 μm. By the final cold rolling, plates of0.15 mm in thickness were manufactured and obtained as experimentsamples for evaluation. The final cold rolling conditions are also shownin Tables 1 to 3.

[0036] Test pieces were sampled from the obtained plates, and thematerials were tested to evaluate “grain size”, “strength”,“elongation”, “bending”, and “electrical conductivity”. To evaluate the“grain size”, the bright fields were observed by a transmission electronmicroscope, and it was determined by the cut-off method of JIS H 0501 onthe obtained photograph. As for “strength” and “elongation”, using No. 5specimens conforming to the tensile test specified in JIS Z 2241, thetensile strength and rupture elongation were measured. As for “bending”,by bend forming using a W-bend testing machine, the bent part wasobserved by an optical microscope at a magnification of 50 times, andpresence or absence of cracking was observed. The mark “o” indicatesthat cracking is absent, and the mark “x” indicates that cracking ispresent. The “electrical conductivity” was determined by measuring theelectrical conductivity according to a four-point method.

[0037] Evaluation results are shown in Tables 1, 2, and 4. The alloys ofthe invention are known to have excellent strength, elongation andbending properties. By contrast, in comparative examples 6 to 8, 14 to16, 33, and 34, since the reduction of final rolling was low, thedesired structure was not obtained, the ductility dropped, and favorablebending properties were not achieved. FIG. 2 is a transmission electronmicroscope photograph of sample No. 12 of the invention, in which themean grain size of the formed continuous recrystallization is 1 μm orless, and its crystal grain boundary is mainly composed of curvedportions and is round. By way of comparison, a transmission electronmicroscope photograph of comparative example No. 6 is shown in FIG. 3,in which the grain size is nearly linear.

[0038] The materials manufactured in embodiments 9, 22, 26, and 30 ofthe invention and comparative examples 33, and 34 were further annealedfor stress relief, and tensile tests were conducted. Results are shownin Table 5. In the alloys of the invention, by stress relief annealing,elongation is further enhanced as compared with that of the alloys ofthe comparative examples. Hence, it is expected to be able to withstandfurther more severe working. TABLE 4 Characteristic evaluation resultsof alloys of the invention and comparative examples Tensile RuptureGrain size strength elongation Bending Conductivity (μm) (MPa) (%)Properties (% IACS) Example of Invention 17 0.40 420 2.5 ◯ 100  18 0.45410 2.7 ◯ 100  19 0.30 420 2.8 ◯ 98 20 0.25 630 2.1 ◯ 15 21 0.45 590 2.9◯ 78 22 0.35 610 2.2 ◯ 74 23 0.25 550 3.6 ◯ 87 24 0.15 670 2.3 ◯ 69 250.30 580 3.8 ◯ 80 26 0.30 590 3.9 ◯ 52 27 0.15 790 3.6 ◯ 50 28 0.20 7802.6 ◯ 52 29 0.35 570 2.9 ◯ 60 30 0.20 540 2.5 ◯ 63 31 0.35 590 2.8 ◯ 5632 0.40 1020  2.4 ◯ 11 Comparative Example 33 Rolled 590 1.2 X 80Structure 34 1.35 800 0.9 X 50

[0039] TABLE 5 Characteristic evaluation results after stress reliefannealing Stress Relief Annealing Conditions Tensile Rupture TemperatureTime Strength Elongation Conductivity Alloy name (° C.) (min) (MPa) (%)(% IACS) Example of Invention  9 400 15 570 8.2 82 22 400 15 590 8.9 7526 450 15 740 9.5 52 30 400 15 520 7.5 65 Comparative Example 33 400 15570 5.1 81 34 450 15 740 4.5 50

What is claimed is:
 1. Copper and copper alloy comprising: a structurehaving fine crystal grains with grain size of 1 μm or less composed ofcrystal grain boundaries mainly formed of curved portions after a finalcold rolling, the structure obtained by dynamic continuousrecrystallization caused by the final cold rolling, and an elongation of2% or more in a tensile test.
 2. Copper and copper alloy comprising: astructure having fine crystal grains with grain size of 1 μm or lessafter a final cold rolling with a reduction η, wherein η is expressed inthe following formula and satisfying η≧3; and an elongation of 2% ormore in a tensile test. η=ln(T ₀ /T ₁) T₀: plate thickness beforerolling, T₁: plate thickness after rolling.
 3. A manufacturing methodfor copper and copper alloy, the method comprising: a final cold rollingwith a reduction η, wherein η is expressed in the following formula andsatisfying η≧3, thereby obtaining a structure having fine crystal grainswith grain size of 1 μm or less after the final cold rolling, and anelongation of 2% or more in a tensile test. η=ln(T ₀ /T ₁) T₀: platethickness before rolling, T₁: plate thickness after rolling.
 4. Amanufacturing method for copper and copper alloy according to claim 3,wherein the copper and copper alloy recited in claim 1 is processed bystress relief annealing, and elongation by a tensile test is improved to6% or more.
 5. A manufacturing method for copper and copper alloyaccording to claim 3, wherein the copper and copper alloy recited inclaim 2 is processed by stress relief annealing, and elongation by atensile test is improved to 6% or more.
 6. Copper and copper alloymanufactured by the manufacturing method of claim
 4. 7. Copper andcopper alloy manufactured by the manufacturing method of claim
 5. 8. Amanufacturing method of copper and copper alloy according to claim 3,wherein the copper alloy is Cu—Ni—Si alloy or Cu—Cr—Zr alloy.
 9. Amanufacturing method of copper and copper alloy according to claim 4,wherein the copper alloy is Cu—Ni—Si alloy or Cu—Cr—Zr alloy.
 10. Amanufacturing method of copper and copper alloy according to claim 5,wherein the copper alloy is Cu—Ni—Si alloy or Cu—Cr—Zr alloy.
 11. Copperand copper alloy of claim 6, wherein the copper alloy is Cu—Ni—Si alloyor Cu—Cr—Zr alloy.
 12. Copper and copper alloy of claim 7, wherein thecopper alloy is Cu—Ni—Si alloy or Cu—Cr—Zr alloy.